The present application is related to Netherlands Patent Application No. 7610598, filed Sept. 24, 1976, the entire disclosure of which is hereby incorporated by reference.
Oxidation processes for the production of phenol from an alkyl benzene compound are described in the literature. In these processes an alkyl benzene compound is first oxidized to a corresponding benzoic acid, followed by decarboxylation-oxidation of the benzoic acid to a phenol compound. For example, it is known that toluene is readily oxidized to benzoic acid by passing air through liquid toluene in the presence of a catalyst at elevated temperatures and pressures. The oxidation of benzoic acid to phenol occurs when steam and air are passed through benzoic acid in the liquid phase in the presence of a catalyst. The phenol produced is carried out of the reaction vessel with the steam and air. Several detailed descriptions of these processes have been published. See Kirk-Othmer Encyclopedia of Chemical Technology, 2d rev. ed., vol. 15, pages 147, 155-156 (John Wiley 1968) and references cited therein.
The term "benzoic acid" as used in this specification include both substituted and unsubstituted benzoic acids, and salts, esters and anhydrides thereof. Similarly, the term "alkyl benzene compound" as used in this specification includes both substituted and unsubstituted alkyl benzene compounds, and the term "phenol" includes both substituted and unsubstituted phenols. For example, the following alkyl benzene compounds may be oxidized by the process described above to the indicated corresponding benzoic acids:
______________________________________ Alkyl benzene compound Benzoic acid ______________________________________ 1,2-Dimethylbenzene 2-Methylbenzoic acid 1,3-Dimethylbenzene 3-Methylbenzoic acid 4-Chlorotoluene 4-Chlorobenzoic acid ______________________________________
In the second step of the two-step oxidation process, the benzoic acid is subject to decarboxylation-oxidation to form the indicated phenol:
______________________________________ Benzoic acid Phenol ______________________________________ 2-Methylbenzoic acid 3-Methylphenol 3-Methylbenzoic acid 2- and 4-Methylphenol 4-Chlorobenzoic acid 3-Chlorophenol and Phenol ______________________________________
See, e.g., U.S. Pat. No. Re. 24,848 to Kaeding, which is hereby incorporated by reference.
The catalytic oxidation of the alkyl benzene compound to the corresponding benzoic acid may be conducted either in the liquid phase or in the gaseous phase. If the catalytic oxidation is conducted in the liquid phase, a cobalt salt which is soluble in the liquid phase is suitable as a catalyst. If the oxidation is carried out in the gaseous phase, a vanadium catalyst may be used. See Stanford Research Institute Reports No. 7, pages 29-33 (1965); No. 7A, pages 241-244 (1968); and No. 7B, pages 53-55 (1976), which are hereby incorporated by reference.
The decarboxylation-oxidation of the benzoic acid formed in the first step to the penol compound may, for example, be carried out in the liquid phase by reaction with molecular oxygen in the presence of a copper catalyst. In addition to the copper catalyst, a magnesium catalyst may also be present. Both the copper catalyst and the magnesium catalyst are preferably dissolved in the liquid reaction phase. Copper benzoate and magnesium benzoate are suitable catalysts. See Hydrocarbon Processing, volume 43, pages 173 ff. (November 1965), and the Stanford Research Institute Reports, No. 22, pages 147 ff. (1967) and No. 22A, pages 113 ff. (1972), which are hereby incorporated by reference.
The decarboxylation-oxidation reaction of the benzoic acid to the phenol compound can be effected by passing a gas containing molecular oxygen through a molten benzoic acid compound or a solution of a benzoic acid compound in an inert solvent, in the presence of a dissolved copper catalyst. The reaction is assisted by passing steam through the liquid reaction phase. The phenol product is carried out of the liquid reaction phase with the molecular oxygen containing gas, and steam. The phenol can then be separated from these gases.
It is also possible to carry out the decarboxylation-oxidation reaction in two steps by reacting the benzoic acid with molecular oxygen in a first step without the addition of steam, to form an ester of benzoic acid with the corresponding phenol. This ester of benzoic acid and the corresponding phenol can be hydrolyzed in a second step by reaction with steam. The phenol product is carried out of the reaction with the steam, and separated. The benzoic acid compound is returned to the first step.
A disadvantage of the above-described processes is that the phenol product obtained is nearly always contaminated with traces of substituted or unsubstituted benzaldehyde compounds and related compounds. The term `benzaldehyde` will hereinafter be used to refer to the substituted or unsubstituted benzaldehyde compounds and related compounds which contaminate the phenol product of the above-described processes. The traces of benzaldehyde present in the phenol product are very difficult to remove, whereas commercially a phenol product low in benzaldehyde is desirable.
The purified phenol product may be subjected to hydrogenation to form cyclohexanols or cyclohexanones, depending upon the reaction conditions, as described in British Patent Specification No. 890,095. The cyclohexanols and cyclohexanones formed by hydrogenation of the purified phenol product of the present invention are easily separated, and are therefore of commercial importance.